Optical scanners, which scan a light flux emitted from a light source such as a laser or a light-emitting diode, are used in practical applications. These optical scanners are classified into a one-dimensional scanning type such as a laser printer or a bar-code reader, and a two-dimensional scanning type such as an in-car radar or a projection display device. For these optical scanners, it is important to detect the position of the mirror surface, and hence, various efforts have been made to provide a monitoring function for achieving this detection.
For example, Patent Literature 1 discloses a method of detecting the position of the mirror surface by providing a light receiving element outside the device, and making the light receiving element receive the light reflected from the device.
Patent Literature 2 discloses a method of detecting the position of the mirror surface by providing a monitoring element such as a piezoresistive element or a piezoelectric element at a position where torsion or bending occurs when the mirror surface is driven.
Patent Literature 3 discloses an invention for detecting the rotation state of the mirror part by providing a piezoelectric sensor connected to the mirror part and to the torsion bar for rotating the mirror part. Patent Literature 4 discloses an invention including a piezoelectric sensor disposed outside the outer periphery of the mirror via a slit in order to solve the problem of Patent Literature 3.